Instruments have heretofore been provided for timing of internal combustion engines which use spark plugs for ignition of a fuel-air mixture. In one type of instrument, a strobe lamp is flashed in response to an ignition pulse which is applied to the spark plug of a certain cylinder, the strobe lamp being positioned to illuminate one or more marks on a damper which rotates with the engine crankshaft and one or more marks on the engine block. With marks which indicate the angular position in degrees, the number of degrees of advance of the spark can be determined by the operator.
In another type of instrument, a delay between the ignition pulse and the flashing of the lamp may be obtained and adjusted until there is an alignment of a pair of primary marks which indicate the top dead center position or "TDC" of the engine. The number of degrees of spark advance is then determined from the magnitude of the adjusted delay.
Such instruments are not suitable for diesel engines in which no ignition pulse is developed. For diesel engines, various types of timing instruments have been proposed but none have been completely satisfactory. In one type of instrument, the injection of fuel into the engine may be sensed at a line leading to an injector. In another, injection is measured at the injector itself. With such instruments, the timing may be measured to obtain valuable information, especially when the sensing is performed at the injector. However, such arrangements do not provide a direct indication of the actual time of firing within the engine.
In an attempt to determine the actual time of firing, instruments have been proposed using fiber optic devices to sense the flash produced upon ignition of the fuel after injection. Such arrangements have been complicated and expensive and have had problems because of a build-up of carbon deposits which preclude reliable detection through fiber optics or the like.
Another problem with respect to diesel engines arises in determining the crankshaft angle at which firing occurs. The type of instrument as used for ignition type engines would not be suitable for diesel engines in which the firing occurs after the top dead center position rather than before. In engines which have provisions for magnetic pick-ups, the position of the pick-ups has not been appropriate for accurate determination of the firing angle even if reliable means were provided for detection of the firing angle.